Patent GB-1195236-A (GB)
Title: Infrared Image Converting Device
IPC: H01L31/14
Filed: 1967-08-07
Abstract: 1,195,236. Electroluminescence. MATSUSHITA ELECTRIC INDUSTRIAL CO. Ltd. 7 Aug., 1967 [15 Aug., 1966; 27 Oct., 1966], No. 36216/67. Heading C4S. An infra-red image converting device comprises an infra-red quenchable photo-conductive layer 26 (e.g. 50 micron thick CdS) the photo-conductivity of which under excitation by bias light is decreased with irradiation of infra-red rays, at least one electroluminescent layer 22, 25 (e.g. 40 micron thick ZnS:CuAl in plastic resin) and voltage supply 28, the bias light being internal feedback from layer 25, the intensity of the feedback decreasing with increase in impedance of p.c. layer corresponding to the intensity of an infra-red input image. Opaque carbon layer 24 and light reflecting BaTi0 3  layer 23 may be both 10 microns thick. Electrodes 21 and 27 are respectively of transparent 5n0 2  and 10 micron diameter W wire of 400 micron pitch or of a plate or plates. Operation with 350V 1 KH 3  A.C. source 28 produces an oscillatory or bi-stable condition with improved contrast and brightness but for high resolution, non-oscillatory or monostable operation with a lower A.C. voltage is required. An external bias light may also be used. Other A.C. voltages and frequencies are discussed. CdS : Cu, Ga, CdSe and GaAs p.c. materials are also disclosed. In Fig. 3 (not shown), E.L. layer 25 is omitted. A dielectric layer (33) may be included. For positive output images, the grid electrode and lower planar electrode may be connected to the same A.C. power supply terminal (48), (Fig. 4, not shown) and further included a transparent 25 micron thick polyester dielectric or ferroelectric layer (400) adhered by a silicone resin, a second E.L. layer (401) of ZnS : Cu, Al in a silicone resin and 5n0 2  electrode (402) on a quartz or glass support layer (403). Layers (401) and (400) may be reversed and layer (400) may be omitted. A translucent layer to control light feedback may be included and may replace layer (400). A second A.C. source of the same frequency may be included between electrodes (41) and (47), and operational characteristics may be varied according to phase and amplitude relationship changes and similar control may be used with modifications in the Figs. 2 and 3 embodiments. The monostable negative output image device in Fig. 5 (not shown) requires no additional external bias light and includes mesh-like gapped or thin metal film electrode (511) of 5n0 2 , a 30 micron thick polyester impedance layer (512), 10 micron diam. W wires (513) in parallel or mesh-like array, a 50 micron thick p.c. layer (514) of CdS activated with Group Ib and VIIb or IIIb elements and in a plastics resin bias light E.L. layer (515), e.g. blue emitting ZnS : Cu, Cl of 30 micron thickness and of spectral emission intensity distribution scarcely overlapping the spectral sensitivity curve of the p.c. layer (514) or the spectral curves may coincide and the E.L. layer of low emission efficiency in order to control the feedback. Also included is high resistance black paint layer (516), dielectric reflecting layer (517), E.L. layer (518) (e.g. green emitting ZnS : Cu, Al in plastics resin and 30 microns thick) and 5n0 2  electrode (519). Second A.C. source S 2  controls the bias light and is in phase with and of the same or different frequency as first A.C. source S 1 . The output image and bias light may be from the same E.L. layer (Figs. 6 and 7, not shown) and feedback may be controlled respectively by layer (601) of carbon black, black paint, or by mismatching of the spectral curves of layer (702) with peak emission of 530 millimicrons and p.c. layer (701) of CdS-Se sensitive to 600 m. micron radiation. The embodiments of Figs. 2, 3, 6 and 7 also produce negative images.